We have found that prostate smooth muscle produces the endothelium specific angiogenesis factor, angiopoietin-1, whereas the epithelium produces its antagonist, angiopoietin-2. We propose that angiogenesis in the prostate is regulated by the balance between signals from vascular endothelial growth factor (VEGF) and the angiopoietins. We will investigate the hypotheses that 1) normal prostate growth is dependent on angiogenesis that is mediated by angiogenesis signals produced primarily by prostate smooth muscle; 2) that formation of aggressive prostate tumors includes loss of expression of the potent angiogenesis inhibitor, angiopoietin-2; and 3) that prostate smooth muscle has an unappreciated role in determining the vascularity and growth of prostate tumors. These studies will make use of a unique panel of mouse prostate cell lines that include prostate tumor cells and normal prostate cells that have been isolated from the same genetic background and a unique model in which injection of combinations of these cells under the mouse renal capsule gives rise to prostate duct-like structures. The prostatic cell lines will be transfected with VEGF cDNA under the control of a reverse tetracycline promoter so that VEGF expression can be modulated independently of androgen levels. In addition, prostate smooth muscle cells will be transfected with anti-sense cDNA to angiopoietin-1, and clones that express decreased levels of the angiogenic factor will be selected. Similarly, prostate epithelial cells will be transfected with antisense cDNA to angiopoietin-2, and clones that express decreased levels of the angiogenesis inhibitor will be selected. Effects of altering the balance between VEGF and angiopoietin expression in these cells on vascular density and growth of prostatic tissue will be determined in castrated and intact animals. Similar experiments will be done with the prostate tumor cells to determine if decreased expression of angiopoietin-2 leads to increased tumor vascularity and more aggressive tumor growth. We shall also determine if decreased expression of angiopoietin-1 in prostate smooth muscle effects vascular density and growth of co- inoculated prostate tumor cells. These experiments will allow us to evaluate the relative contribution of smooth muscle-derived endothelial cell ligands to angiogenesis in prostate tumors. Identification of angiopoietin-1 or angiopoietin-2 as a key mediator of angiogenesis in the prostate may lead to new treatment strategies for both androgen-sensitive and androgen- independent prostate tumors.